Purge Flow Monitor

Perform the following:

• A Purge Free Cell Update must take place.
• A/T transmission is in gear at idle, Cell 12, or M/T is in Cell 13.

To perform a Purge Free Cell Update:

• The engine must be running in Closed Loop.
• Engine coolant temperature above 170°F for more than 1 minute.
• The PCM attempts a Purge Free Updated every other time the Cell is entered.
• The engine must remain in the Cell for 20 seconds to complete a Purge Free Update.
• The Purge Free Cell will update once the Purge Duty Cycle returns from 0% to some other value, and the PCM begins Stage I of the Purge Flow Monitor.

Stage I:  If any of the Purge Normal Cells are richer than their Purge Free Cell Mirrors by the calibrated amount, Stage I Passes. Stop testing this trip. Stage I Pass Specifications. If less than the specification, continue with Stage II.

Stage II:  Perform the following:

• Delay for 1 second from Stage I.
• Minimum BARO more than 21.70".
• Maximum Throttle Change (TPS) less than .060 volts.
• Maximum MAP vacuum change less than 0.50" vacuum.
• Maximum RPM change less than 96 RPM.
• Maximum charging system voltage change less than 0.99 volts.
• Maximum generator duty cycle change less than 14% duty cycle.

The PCM updates the Cell with purge on for 1 second. The PCM updates the Cell with purge off for 2 seconds. In Stage II, the PCM subtracts the Purge Normal Cell value from the Purge Free Cell Value. If the difference is greater than calibrated amount, Stage II Passes and no further testing is performed that trip.

If the difference is less than the calibrated amount, continue testing. The PCM averages the Short Term Adaptive Memory percent and the RPM for 3 seconds. The PCM stores the averaged Short Term Adaptive Memory and the RPM value and then reads and stores the IAC Steps. The PCM begins increasing the Purge Flow (by increasing the Purge Solenoid Duty Cycle) .40% every 44 milliseconds. The PCM begins a new averaging for Short Term Adaptive Memory and RPM. The PCM continues taking new IAC step readings. The PCM compares Short Term Adaptive, RPM and IAC Steps from before the Purge Duty Cycle was increased during Stage II until 1 of 3 things happen:

• Short Term Adaptive % changes by 5.0%.
• IAC Steps change by 1 Step.
• RPM changes by approximately: 100 RPM

If any of the above happen, Stage II passes. If not and 99% Purge Solenoid Duty Cycle is reached, Stage II Fails. This will cause the Purge Flow Monitor to Fail 1 Trip and Freeze Frame Data will be stored.